Margot Kidder, the vivacious actress who played Lois Lane opposite Christopher Reeve in the Superman movies and then waged a public battle with bipolar disorder, has died, her manager, Camilla Fluxman Pines, confirmed to USA TODAY. She was 69.

Fluxman Pines told USA TODAY that Kidman "died peacefully in her sleep Sunday." She did not give the cause of death.

Margaret Ruth “Margot” Kidder, born in Yellowknife in Canada's Northwest Territories in October 1948, was Canadian and American, an actress and an activist.

Margot Kidder in her role as Lois Lane shares an intimate champagne supper with Christopher Reeve as the Man of Steel in the film 'Superman II.'(Photo: Associated Press)

She started out in the 1960s in low-budget Canadian films and TV series, then hit the big time in 1978 with her role as perky reporter Lois Lane in Superman. She also appeared in the three sequels.

She was aware from an early age, according to her diaries, that she suffered from constant mood swings, and even tried to kill herself as early as age 14. By the time she became a movie star she had sunk into the throes of paranoia and what she would learn was bipolar disorder, a condition characterized by "up" and "down" phases in which the patient experiences periods of elation or mania, followed by bouts of severe depression.

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Clark Kent, aka Superman, as portrayed by Christopher Reeve, and Lois Lane, portrayed by Margot Kidder, left, are mugged by an armed man in an alleyway during a "Superman" scene filmed in New York City on July 8, 1977. AP

Margot Kidder and Christopher Reeve pose in front of Oscar at the 51st annual Academy Awards in Los Angeles on April 9, 1979. Kidder portrayed Lois Lane opposite Reeve in "Superman." The movie received a special achievement award for visual effects, plus nominations for film editing, original score and original sound. REED SAXON/AP

An undated file photo of Margot Kidder, distributed when she went missing for three days in April 1996. She was found in a backyard in Glendale, a suburb of Los Angeles, looking dirty, unkempt and missing two front teeth, and was taken in for a 72-hour psychiatric evaluation. AFP/GETTY IMAGES

Supporters Margot Kidder, left, and Chris Bruha celebrate after receiving news that the Democrats gained the majority of the U.S. House of Representatives and that Jon Tester defeated Republican incumbent Conrad Burns during a Park County Democrats election day party at The Murray Hotel in Livingston, Mont., on Nov. 7, 2006. GARRETT CHEEN/THE LIVINGSTON ENTERPRISE/AP

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In April 1996, she disappeared and ended up living on the street for a period of days. A search was launched after she was reported missing when she failed to board an airplane.

Kidder eventually was found "dirty, frightened and paranoid," hiding in the bushes of a suburban backyard in Glendale, Calif., according to police at the time. She was taken to a psychiatric hospital for observation.

"If anything unfortunate happened to Margot, my heart goes out to her," Reeve said in a statement. "She is a dear friend who has always been there for me, and I would do anything to help her." (Reeve was paralyzed in a riding accident in 1995, and died in 2004.)

At the time of her disappearance, Kidder had been working on an autobiography, but her laptop was infected with a virus, causing her to lose three years' work. When the files could not be retrieved, she fell into a manic state and disappeared in the Los Angeles area.

When she was taken to Olive View Medical Center, the caps on her teeth were knocked out, the result of a rape attempt.

Kidder later started advocating for mental health awareness. In 2007, she said she had not had a manic episode in 11 years, and credited her health to alternative medicine through nutritional supplements.

She continued working, however. In 2015 she earned a Daytime Emmy Award as outstanding performer in a kids' series for R.L. Stine's the Haunting Hour.

"I don't act much anymore unless I'm broke, and then I'll take a job," she told a Detroit radio station with a laugh.

She spent the last decades of her life living in Montana and engaging in political activism as a liberal Democrat, including protesting U.S. military action in Iraq.

Kidder is survived by her daughter, Maggie McGuane, with her first husband, American novelist Thomas McGuane, and two grandchildren from her daughter's marriage to novelist Walter Kirn.

Kidder was married to actor John Heard in 1979 for six days, and to French film director Philippe de Broca from 1983 to 1984.

Colin Zeman, a spokesman for the Franzen-Davis Funeral Home in Livingston, near Bozeman, Mont., said funeral arrangements for Kidder are pending.